Device for reproducing cinematographic image records



y 28, 1940- I R. LEVY DEVICE FOR REPRODUCING CINEMATOGRAPHIC IMAGERECORDS Filed Sept. 22, 1936 2 Sheets-Sheet 1- ,lnvenzar May 28, 1940,LEVY DEVICE FOR REPRODUCING CINEMATOGRAPHIC IMAGE RECORDS Filed Sept.22, 1936 2 Sheets-$heet 2 Inventor Levy (73 $2. I f m Attorney PatentedMay 28, 1940 PATENT OFFlCE DEVICE FOR REPRODUCING CINEMATO- GRAPHICIMAGE RECORDS Rudolf Levy, Bel'lin-Halen'see, Germany ApplicationSeptember 22, 1936, Serial No. 101,911 In Germany September -30, 1932 5Claims. (CI. 88-17) The invention relates to a device for reproducingcinematographic image records by means of optical stoppage of thecontinuously moved series of images by instantaneously making vis- 5ible the individual images.

In the known devices of this kind is made for the step by stepillumination of the continuously moving cinematographic images of aconstantly burning source of light, whose light flow is caused to becomeactive briefly through the slots of a shutter disc or drum movable withconsiderable speed in front of the same, particularly by rotation. Inother devices of this kind continuously illuminated and continuouslymoved 18 series of images are projected for short time intervals' forsecuring the cinematographic picture eflect, in that such'a shutter isinterposed in the The speed of course of the projection rays. movementof the shutter disc or the like is therego by controlled by directconnection with the image support driving means or alsoelectromagnetically in dependence upon the movement of the image recordcarrier in correspondence with the speed of change of the image.

The duration of the individual illumination or projection light flashes,which may amount to only a very small fraction ofthe image interchangeperiod, is hereby clearly dependent mainly upon the speed with which theshutter open- 1 ings cut the path of the light rays which in practiceresulted in the requirement that discs or drums of verygreat-circumference had to be used. Moreover, the-narrower the slit ismade, the more sharply defined will the pictures be 35 seen, but'correspondingly weaker will be thelight as is well known, and finallythere is also a certain lower limit for the size of the shutter openingsbelow which. it is impossible to go, because then distortion effectsoccur at the edges of the shutter openings. Sharply defined andsatisfactorily steady cinematographic images on the screen can thereforenot be secured in this way. The present invention has for its object toimprove devices of this type in that for the brief 45 interruption ofthe light there is interposed in the path of projection an electricallycontrolled light valve whereby he intensity .and duration of thequantity of lig t at any time transmitted, with a given constantlyacting light source, are 50, dependent essentially upon the magnitudeand duration of the very short electrical impulses controlling the lightvalve.

For closing or instantaneous opening of the light path according to thepresent invention, 55 there are eminently suitable such electrical lightvalves which depend upon the use of the electrooptical ormagneto-optical effects upon polarized light, particularlyin the form ofKerr cells with electrical double refraction or Faraday cells withrotation of the plane of polarization of the light, 5 which follow themagnitude: and instantaneous value of the applied short impulsespractically without inertia. According tothe invention, the electricallight valve may be interposed in the illumination or also in theprojection path of 10 the rays.

The mentioned lighting like impulses of potential or current may, inaccordancewith the .invention, be produced by means of a condensertripping device byvimpulse discharge of the con- .denser and also withgreat exactness with reference to their succession and may-be broughtinto concidence with the image change. I

The invention is, however, not to be considered as limited with respectto the manner of pro- 20 ducing electrical impulses.

By means of the invention there may be attained at once the-necessaryexact starting point as well as anextremely short period of brightnessbetween the starting and stopping of the light transmlssion,"foravoiding'the distortion and flickering of the projected cinema picturesand by using the Kerr or Faraday cells already mentioned if necessarythe simultaneous sound reproduction will not be disturbed.

The invention is also especially advantageous for home cinema projectorsand especially in such intended for continuously rotating disc or drumshaped image record carriers, upon which small cinema pictures in largenumber are recorded in adjacent series, for example spirally orcircularly arranged. As a result of the special image arrangement, whichin operation requires a relative shifting of the reproducer element andthe image record support with. respect. to one another, as well as dueto the necessarily small size of the image usually amounting to only .afew millimeters, and also as a result of the necessary restriction inthe size of the construction, in these devices particularly severestructural difficulties must be overcome for optically stopping ormaking stationary the continually shifting series of images.

Since with simultaneous sound and picture, reproduction in home cinemadevices of this type th picture receiving screen is ordinarily set up intheimmediate vicinity of the producing apparatus or even structurallycombined there-' with, the noiselessness of 2. Kerr or Faraday cell foruse as a light valve is particularly advantageous. Such cinemaapparatus, although because of their nature, particularly their simplemanipulation and the form of the image record carrier they appealed tothe public and to a great extent met the requirements and customs, werepractically heretofore not capable of application. Only'by thepresentinvention has material progl0 ress been secured in order to make these,cinematographicdevices simple and useful and thereby open the path totheir general use.

' In the accompanying drawings, the invention is shown diagrammaticallyas based upon possible embodiment and in said drawings.

Fig. 1 is a, diagram of an arrangement in accordance with the inventionemploying a Kerr cell and Fig. 2 one employing a Faraday cell as thelight 0 valve in'the path of the illuminating rays.

Fig. 3 shows the arrangement with a light valve in the path of theprojection rays.

Fig. 4 shows the arrangement in a reproducing] device for disc shapedimage record carriers with spirally arranged series of images and Fig. 5is an elevation of the complete device.

In Fig. 1 the condenser I is charged through the resistance 4 from adirect current potential applied to the terminals 2 and 3 and isdischarged through the tube 5. The discharge commences when the voltageat the condenser has attained such magnitude that the negative gridpotential of the tube 5 is overcome.- Simultaneously the anode currentin tube 1 is stopped by the resist- 3'5 ance.6.- Thereby the negativegrid potential of tube 5 returns to zero, which further speeds up thedischarge. If shortly before the discharge there be applied'to the tubeI a potential impulse through the transformer 8 in such way that the 0tube 5 receives a positive grid potential, then the discharge phenomenonwill be initiated early. This connection is already known in another artand for other purposes.

The film strip II is illuminated by means ofa light source l2, forexample an incandescent projection lamp, a metal-vapor high pressurelamp, or the like, and by an optical condenser l3. I4 and I5 arethesupply and take-up reels between which the fllm,strip is continuouslymoved. In the,path of the illuminating light rays between the lightsource l2 and the film strip II is interposed a Kerr cell arranged as anelectrically controllable light valve, consisting of the crossedNicols I6, I1 and the plates l8, 19 of the Kerr condenser between which there isa suitable transparent medium, for example nitrobenzol or suitablecrystals. There is further provided another optical condenser 20. v

If alternating current whose frequency corresponds to the rate of imagechange of the constantly moved film strip ll, be supplied to thetransformer 8 through the terminals 9 and It then .the trip oscillation.is synchronized. The discharge current; consisting of widely spacedstrongly peaked impulses, is conducted through the transformer 2| to thecondenser plates l8, I9

of the Kerr cell. Since the light allowed to pass through the analyzerI1 is a function of the voltage at the Kerr cell, the device may bereadily so arranged that each discharge impulse causes a brieftransmission of the light flux from. the source of light [2. r r

The short light flashes thus produced illuminate the continuously movedfilm strip ll whose cinematographic images may hereby be stoppedilluminating light flashes.

or brought to a standstill by optical means and projected into space bymeans of the optical system 22. A normal voltage of such value may beapplied to the plates of the Kerr condenser that a slight illuminationnormally occurs, which, however, does not suflice to illuminate theimage series on the film strip ll. so strongly that they would bedisturbingly visible upon the projection screen during the dark"intervals; this initial potential would then have superimposed upon itthe sudden abruptly applied electrical impulses. For eliminatingundesired charges of the Kerr condenser, there may be connected inparallel therewith, if desired, an electronic or ionized discharge gap,for example a glow lamp.

Fig. 2 shows an arrangement wherein a magneto-optical light valve isused for producing the A condenser 26 is charged through a resistance25, by means of a direct current or a rectified current, applied to theterminals 23 and 24, which condenser discharges through the coil 21 andthe electron tube 28, when an alternating current voltage is applied tothe grid 29 of the latter, through terminals 30 and 3l,-and synchronouswith the picture change rate. The coil 21 sur-.

, rounds a tube filled with carbon disulphide or a cylinder 32 madeofFaraday glass. 33, 34 are polarizer and analyzer. 35 is the constantlyactive source of light and 36 is an optical condenser system. The twoNicol prisms 33, 34 are so adjusted with respect to one another thatJust no, or only little, light transmitted therethrough. Upon eachdischarge of the condenser 26, through the winding 21, a current impulseof short duration flows through the same and a rotation of the planeof'polarization occurs and therewith an instantaneous brighteningoccurs. By means of the light flashes thus produced, through the opticalcondenser system 36, the continuously traveling film strip 31 is brieflyilluminated, its thus optically stopped individual series of picturesbeing projected into space by the optical system 38. In the ,device justdescribed intense magnetic fields of short duration may be produced,instead of by the electron tube 28; also in known manner by means of gasdischarge lamps, for example by means of mercury vapor tubes, whosecurrent flow is suitably controlled. For example, such a gas dischargetube may be fed at definite intervals by a condenser connected inparallel therewith, which is charged" through a resistance within onepicture-change interval, by impulse discharge of the condenser, wherebythe trip. starting of the condenser is controlled, for example through acontrol electrode, within or with-j out the gas discharge lamp or bymeans of-.a thyratron. The condenser discharge may also take place forexample through a mechanically controlled spark gap. It is further alsopossible to control both the moment of tripping of the condenser and thedrive motor for the image carrier directly from the same alternatingcurrent supply system; or for example through frequency changers. v

Fig. 3 shows an arrangement in accordance with the invention wherein theelectrically controllable light valve is interposed in thepath of theprojection rays.

The series of images on the continuously moved film strip 39 areilluminated by the source of light 40 through the optical'condenser 4|and projected upon the screen 43 by the optical system 42a. In the pathof the projection rays'is interposed the light valve, and the rays aremade 7 -llke alcohol or grid electrode 45, through a sheetlike layer 46of doubly-retracting material and through a second sheet-like alcohol orgrid elec-' trode 41 as well as through the analyzer 48. The sheet-likelayer 45 of doubly-refracting material may consist, for example, of aplurality of assembled crystal plates of zinc blende. The Kerr cell mayalso be made in the form of a sheet-like multiple plate condenser,instead of being made of the sheet-like layers 45, 43, 41, preferably inthe known type of thin metal strips of alternate polarity whichinterengage in comb fashion and between which the doubly-refractingmaterial is located. v

Sudden electrical impuses are fed to the terminals 45a and 41a of the 45and 41, which upon suitable dimensioning and adjustment of theoptical-electrical cell produce their optical opening forbriefintervals, that is, permit the transmission of the light flux ofthe projection light source, and such sudden impulses are produced bythe device hereinafter described. The condenser 52 is charged from analternating current source connected to the terminals 49 and 50, througha rectifier and a small gas discharge lamp 53 is connected to theterminals of said condenser in series with the primary winding of asmall high tension transformer 54. The gas discharge tube 53 has adefinite starting voltage and a materially lower operating voltage. Upondischarge of the condenser 52 through the gas discharge tube 53 and theprimary winding 'of the transformer 54 a voltage impulse is produced inthe secondary side of the latter which is fed to the transparent sheetelectrodes 45, 41

of the light valve The discharge frequency is determined by the time ofcharging and may be controlled by a resistance connected in the chargingcircuit or by changing the cathode temperature of the rectifier tube 5|,and made to agree with the rate of picture change. Of course, hereby thedischarge frequency of the tripping capacity 52 may also be synchronizedin agreement with the movement of the picture strip 39 in another way,for example by controlling the gas discharge tube 53, say, by means of acontrol grid.

The short electrical impulses fed to the light valve may also beproduced in another way, for example by interrupting the current on theprimary side of an induction'coil in synchronism with the rate ofpicture change, whereby on the secondary side voltage impulses areinduced which act upon the light valve, or also by means of a rotatinggenerator working'on the induction principle, which is mechanically orelectrically connected with the driving means of the image recordcarrier.

Figs. 4 and 5 show an example using the invention in a cinematographicreproducing-device for disc-shaped iinage record carriers.

Fig. 4 shows in section a picture arm for a reproducing device such asshown in Fig. 5. The light valve 55-a Kerr cell or its equiva1ent-ishere arranged rigidly in the vertical pivot 56 of the swinging arm 51and has the optical condenser system 63, the polarizer 58 and theanalyzer 59 as well as the condenser plates 50 and 5|, between which thedoubly-refracting material is located. Short voltage impulses areapplied to the terminals 60a and Bla of the Kerr-cell by means of one ofthe above-described devices. The light valve 55 is arranged stationarywithin the housing 52.

transparent electrodes The light from the source 64 which brieflytraverses the Kerr cell 55 when electrical impulses are applied thereto,is concentrated by the optical system 55 upon a small window frame 55arranged in front of the light valve 55. By means of the lens system 51,an image of the frame opening 56 is thrown upon the sheet-like imagerecord carrier through the mirror, prism, .or the like 68 mounted in thevertical axis of rotation of the swinging arm 51, and a further mirror69 from which image recordthe light is thrown back to the adjustableprojection objective 1i. This projection objective is arranged in thehead of the swinging arm 51 and transmits the light to a furtheruniversally adjustable mirror 12 which throws the picture upon theprojection screen. An interchangeable guide pin 13 serves "Tor guidingon the image record support 10, the

arm 51, whose forward portion 51a may be foldable upwardly, said guidepin 13 sliding in a spiral groove 14 which runs adjacent the likewisespirally arranged little images 15. Y

The swinging arm pivot 55 is rotatable in a guide ring and is there heldby a bail, .which is secured by means of a readily releasable screw 16.After releasing the screw 16 the swinging arm may be lifted off upwardlyin such manner that the light valve 55 and the light source 64 arereadily accessible for changing The constant source of light, theoptical system and the electrical light valve may be built into a vsmall unit and be interchangeable with respect to the latter by specialsecuring means. A common base plate may serve as a support for the partsthus combined into a whole. This unit may, in reproducing apparatus fordisc-shaped image records, be provided series of images (similar toFigs. 4 and 5) and may also be arranged as an illuminating unit withinthe hollow swinging arm or on the head of the latter. Anotherpossibility which serves particularly for reproduction of transparentimage spiral discs would consist in arranging the illuminating unit uponthe lower or upper tines of a fork which is swingablyor shiftably guidedabove the image records u'pon whose second tine, opposite theilluminating unit, the optical projecting system is arranged.

Finally, it is also possible with the described unit at any time toilluminate in common an entire radial series of the" individual imagesarranged at uniform angular spacing from one another upon the imagespiral plate, whereby at any time only a single image of this series isactually used. For this purpose the light proceed is projected by meansof a cylindrical lens optical system, say, in the shape of a smallrectangle upon a radial series of images and illuminates the latter. Itis hereby also possible to use a constant light source with alongitudinally extending incandescent filament, for example a tubularincandescent lamp, a high pressure mercury vapor tube or the like, aswell as a Kerr cell, with two closely adjacent condenser'plates, whoselength dimension corre sponds to the length of a radial'series ofimages, or of the cylindrical lens. If the individual images of thecinematographic record series are associated with one another in anarcuat ely bent line in such manner that their utilization is made withspirally arranged a oppositely arranged or the strip-like diaphragm maylikewise be given ring or the like an arcuate curvature so that theimage produced by the cylindrical lens system is likewise curved andcorresponds to the curvature of the radial series of images. N I a Thereceiving optical system moving in accordance with the operation inthese cases is preferably provided with a diaphragm which has a lengthdimension of such magnitude that those images which havenot yet beenprojected aswel'i as those already utilized of those individual pieturesin a radial series of images which are il luminated in 1 common, arecovered thereby in order that thestray light which would otherwisecreate a disturbance will be eliminated. In order to .iaciiit'ate thesetting of 'the optical receiving they are rather intended to explainonly the most I important considerations and severalstructuralarrangements of the device inaccordance with the invention. Importantauxiliary details, which, however, are of less value in characterizingthe invention, have vbeen either entirely omit- I ted for greaterclearness or else designated merely by simplified symbols.

I claim: 1. Device for reproducingv cinematographic image records,especially on disc or cylindrical record carriers,. particularly i'oramateur cinema ing nitro benzol as the dielectric.

use, by optically stopping continuously moving series of images andthusl momentarily making visible the successive individual images to beprojected, said device consisting of means for constantly illuminatingtheimages, a transparent flat plate or layer of electro-optically activev material which-is arranged between two polarizing sheets, twosheet-like transparent electrodes for controlling the instantaneoustransmission of light of said material by means of electrical impulsesof very short duration, means for producingsuch impulses by condenserdischarges, 01' a frequency corresponding to the desired rate ofimage-change, all said sheets and electrodes being inserted in the pathof the rays of the pro- .iection light between the image,carrier and theprojection screen.

2. Device in accordance with claim 1, wherein the eiectro-opticallyactive material is a plate or layer consisting ofa plurality of separatecrystals 1 of zinc blende assembled into a relatively large surface. v'3. Device in accordance with claim 1, wherein the electro-opticallyactive plate or layer consists of a flat multiple-plate electricalcondenser having a doubly-retracting medium as the dielectric. .4.LDevice in accordance with claim 1, wherein the electro opticaliy activeplate or layer consists of a flat multiple plate electrical condenserhaving thin armatures intere'ngaging with one another in comb-likearrangement; andhaving a double-retracting medium as the dielectric.

5. Device in accordance with claim 1, wherein the eiectro-opticallyactive plate or layer consists of a flat multiple-plate electricalcondenser hav- RUDOLF LEVY;

